Cathode ray tube current amplifying means



Sept. 2, 1958 J. T. MCNANEY 2,850,657

CATHODE RAY TUBE CURRENT AMPLIFYING MEANS 2 Sheets-Sheet 1 Filed Aug. 20, 1956 Pow/E12 SUPPLY CONTROL c/Qcu/Ts F115; 2 FILL 5 INVENTOR. JOSEPH I MCNANEY ATTORAEY Sept. 2, 1958 J. 17. MONANEY 2,850,657

' CATHODE RAY TUBE CURRENT AMPLIFYING MEANS Filed Aug. 20, 1956 2 Sheets-Sheet 2 POWER SUPPLY CONTQOL c/eculrs V 92 PULSE ae/viedrae 9o DEIIECT/ON PL ATE SYSTEM/8 70 DEF ECT ON 72 F1E' 6 IN V EN TOR.

Jose/w 71 MCNANEY.

ATTQRW United States Patent CATHODE RAY TUBE CURRENT AIVIPLIFYING NIEANS Joseph T. McNaney, La Mesa, Califi, assignor to General Dynamics Corporation, Rochester, N. Y., a corporation of Delaware Application August 20, 1956, Serial No. 604,931

7 Claims. (Cl. 313-65) This invention relates generally to apparatus for amplifying the useful current of a beam of electrons in a cathode ray tube. More particularly theinvention relates to means by which the electron emission or current density of a photo-cathode may, in effect, be increased over that initially available from such a source.

In my application for patent, Serial No. 568,236, assigned to the common assignee hereof, a device utilizes a primary electron beam which is derived from a photoemissive cathode. The photo-emissive cathode,,however, has a rather low current density output with limited utility. The device will have greater utility if the intial current density obtained from the photo-cathode can be increased over that presently available. This becomes important when the device is utilized inhigh-speed image display applications, either for visual or recording purposes. In such applications the relatively low current availability of the photo-cathode has been found to be inadequate.

The present invention overcomes the stated. inadequacy by novel combination of means for increasing. the current density of photo-cathode tubes. The invention utilizes a photo-emissive cathode similar to that described in my application Serial No. 568,236, and effects current amplification of the cathode emissionv to increase target response to the information to be presented.

The invention includes several embodiments and envisions the use of an assembly of large numbers of such devices or tubes in rows and columns for display board purposes. It should be clearly understood that the in vention isv not limited tosuch use, but that such use is illustrative of an application of. the invention. In applications of this kind, it may be desirable to display messages by means of large size individual characters. on the viewing screens of individual display tubes. It. is also desirable that the, characters displayed be retained on their viewing screens until selectively erased.. Still another requirement in applications. of this kind-is to have available for display on any one tube screen a Wide selection of message symbols. In character beamshaping tubes using internal beam shaping means, the. practical limitbuilt into any single envelope at present is under one hundredseparate symbols. In view of the limitation of these types of tubes, and the requirements of the application. referred to, the variety and quantity of symbols made availablefor display purposes will be under control of optical equipment external to the envelope as. referred. toin the-related patent application. The. message characters will then be projected onto the. photo-emissive cathode. to effect energization'thereof.

It is, therefore, an object of this invention to providea new. and improved means of amplifying photo-cathode currents of a cathode ray.

t is another object of this invention to increase thev cur rent density of an information-carrying electron fiow from a photo-cathode to improve the target response to the information.

It is another object ofthisinventionto amplify electron "ice flow derived from a photo-cathode by modulating a second source of electrons in accordance with the cross-sectional shape of the photo-cathode currents.

It is still another object. of this invention to modulate a secondary electron beam with a character shaped electron fiow derived from a photo-cathode.

Objects and advantages other than those set forth will be apparent from the following description when read in connection with the accompanying drawings,v in which:

Figure l is a diagrammatic cross-section of a cathode ray tube utilizing a photo-emissive cathode and embodying a novel amplifying means;

Figure 2 is an enlarged view in cross-section of the novel amplifying means of Figure 1;

Figure 3 is a partial cross-sectional view through the conductors of Figure 2;

Figure 4 is a diagrammatic cross-section of an additional embodiment of a cathode ray tube utilizing a photoemissive cathode and employing another novel amplifying means;

Figure 5 is an enlarged partial view in cross-section of the electron current amplifying means of Figure 4;

Figure 6 is a partial view in elevation of the emitting surface of Figure 7;.

Figure 7 is an enlarged detail view of the emitting means of Figure 4.

Shown in Figure l is an evacuated container 10 which may be of any desired shape and made of any desired material such as glass, plastics, metals or combinations thereof. The. preferred embodiment is shown generally in the shape of. a normal cathode ray tube, however, the container size and shape may be as desired and still be encompassed in. the present invention.

Forming one end of the container 10 is an optically transparent Window 11 which has supported on its inner surface a photo electron emissive cathode or means 12. The photocathode 12 may be made of any known photo emissive material such as caesium, lithium, potassium, sodium, either coated on silver or like metals or directly on glass, but uses in the preferred embodiment the caesium-silver oxide type of emitter. Photo-cathode 12 may be excited by any light source external to the container (not shown, but described in Serial No. 568,236) and is capable of generating a beam of electrons or electron flow 1-4 in response to such excitation for projection along longitudinal axis 15. In cooperative relation with the photo-cathode 1-2 there is positioned within container 10 an electron lens 13, which may be either electrostatic or electromagnetic and is shown as electrostatic. Lens 13 directs the beam. of electrons 14 emitted from the photocathode. 12 to the surface of a stepping element or apertured electrode 16 presenting an aperture. The cathode 12 together with lens 13 form the means for generating and projecting electron flow 14.

The instant invention improves'the assembly of electron beam control elementsreferred' to and those shown and described in my patentapplication Serial No. 568,236, among other improvements and. advances in the art, in that a beam current amplifier unit or electron flow amplifying; means 17 is placed generally adjacent the apertured electrode 16 on the side of the electrode facing the target to effect amplification of the electron flow. A first deflection system or means 13 positioned intermediate the photo-cathode means and the apertured electrode, which may be ofelectromagneticor electrostatic construction is shown hereas electrostatic, utilizing deflection plates 18. Plates 18, which may be: coplanar as shown, are supplied with control voltages from control circuits 19 to effect positioning of a desired portion of the beam 14 through the aperture. of electrode: 16 andup'on a control surface assembly 21. of the beamcurrent amplifier 17.

. versely thereto.

photoconductor layer 24, such as' selenium. It' should be understood that a variety of diiferent known materials could be used for 22, 23 and 24, and such known materials are included herein. The control surface assembly 21 is supported in sandwich type construction and positioned generally coaxial with the axis and trans The phosphor 22 faces cathode 12, layer 24 faces the target, and, in between the two in contiguous relation therewith, is the conductor layer 23. The control surface assembly 21 has positioned contiguously with the photoconductive layer 24 a plurality or assembly of conductors 29, each isolated electrically j from the other by electrical insulating material 30, in-

cluding such known insulators as rubber, glass, ceramics, plastics, and the like. Carried or disposed upon each of the opposite ends of the conductors 29 is a thermionic electron emissive material forming a plurality of individual or discrete thermionic emissive elements or thermionic emitters or cathodes 31. The elements 31 may be selectively connected to a negative current source through a lead 32, conducting layer 23 and conductors 29, under the control of photoconductive layer 24. The beam 14 emanatingfrom photocathode. 12, elfects bombardment of'the phosphor 22, which changes electron bombardment to light, and the-light through trans- 'parent layer 23 selectively causes layer 24 to become conductive. The corresponding conductors then cause the .thermionic emitters 31 to become excited, the negative potential from lead 32 being presented thereon. The emitter 31 is raised toan operating temperature by the transfer of heat from a heater unit 35 which is supplied with electrical energy by conductors 36 and 37. A reflector 38 may be provided to concentrate the heat gen- 7 erated by heater 35 on the emitters 31, thereby, improving 'the efiiciency of heat transfer. Reflector 38 may, in addition, serve as one of the control elements of a lens system 40. a

Lens system 40 may be'electromagnetic or electrostatic, but is shown as electrostatic, and is used to direct the electron beam emitted by the thermionic cathode along a predetermined path within the envelope 10 generally coaxial with axis 15. A second deflectionsystem 41 which may likewise be electromagnetic or electrostatic is shown as electrostatic, and is provided to effect control of the electron beam from emitter 31 and to direct the beam toward any desired location on a target 42. Target 42 may be supported on the inner surface of a window 43 of the envelope 10; The target 42, may be electrically responsive or may be an electron to light converter, and is shown as the latter utilizing any of the 'ment 16 and upon control assembly 21, by means of the lens system 13. Since the electron flow 14 may contain a plurality of message symbols, deflection system 18 permits selection of a portion of the electron flow having any one of the desired symbols or a combination of such message symbols and to position that portion on the control surface assembly 21 of the amplifier unit 17. The currenteontent of the selected portion of the electron fl0w,14 praythen beincreased, or decreased,

in accordance with the design requirements of the ampli 'fier unit 17.

In the absence of electron flow 14 to excite the phosphor 22, the passage of current from the conducting layer 23 to the emitters 31 will be zero, due to the dark resistivity of the photoconductor 24. Therefore, when the phosphor 22 is excited by the electron flow 14, the

.resistance' of the photoconductor 24 will be lowered in accordance with the light ray pattern reaching its surface from the illuminated phosphor 22. A resultant gain in beam current is a function of the electron potential in the electron flow 14 at the time of contact with the phosphor 22. The resultant current gain or ultimate beam i beam emitted from cathodes 31.

density may also be a function of the size of the area of control surface assembly 21 ,that is bombarded by electron of the electron flow 14.

The cross-sectional dimensions of the amplifying means 17 exemplified in Figures2 and '3 may be determined by the application of the device. For example, if message symbol beams 0.010 inch respectively, are emitted by the photo-cathode 12 and it is desirable to have such beams appear, independently, on the surface 21 at least ten times these dimensions, then the diameter of the amplifier unit 17 would have to be large enough to accommodate a 0.1 inch 2 symbol. The number of conductors 29 required in an application or this kind would depend on the desired resolving power of the secondary It is possible in this manner to identify a Wide variety of message symbols utilizing a raster of 10 x 10 conductors 29.

' High accelerating potentials may be administered to the electrons selected from the beam 14 by an additional anode 45, in combination with potentials applied to conducting layer 23. It may also be obvious to those skilled in the art to utilize a fine wire mesh in the case of the accelerator elements 16 and 45. Wire mesh accelerators may provide a more compact and more efiicient sys- 1 tem for energizing the phosphor 22.

A second embodiment of the invention is shown in V Figure 1, except that the aperture 46 provided in stopping plate or apertured electrode 16, is large enough only to allow a predetermined portion of the electron flow 14 to enter the remaining portion of the envelope 20 toward i 1 the target area 51, 52. In addition, this'embodiment utimay have a face plate 50, and as shown in detail in Figure 5, may also have a target or phosphor screen 51 disposed thereon, with a metallized backing 52, such as I mesh 53 spaced from backing 52, a collector screen 54 aluminum, disposed on target 51.

Positioned generally adjacent the target, and, in spaced relation therewith, is a storage means. The storage means comprises generally an electrostatically chargeable storage spaced from mesh 53, a beam intensifier 57, a barrier mesh 58, each spaced from the other and disposed in a sandwichlik-e construct-ion generally coaxially disposed about the axis in the order stated from target toward c'athode.- Positioned adjacent the apertured electrode 16 and facing the target is a thermionic emitter 60, similar in emitting materials to be used for emitters 31, namely, known emitting materials including thorium oxide, barium oxides and the like, and capable of generating and projecting an electron beam 64 generally coaxial with theaxis. 'In order to position emitter 60 substantially coaxially with the axis 15, it may be made annular in shape and placed adjacent and about the aperture 46 as shown in detail in Figures 6 and 7. Intermediate the 'emitter 60 and the storage means is disposed, generally coaxially with the axis, an electron lens. The electron lens, as is well known in theart, may be electromagnetic '5 or electrostatic, but for purpose of illustration is shown as an electrostatic lens 56.

The cathode ray apparatus of Figures 4 and '5 may be used in combination with an input information light source and system control means similar to that shown in my application Serial No. 568,236 as aforestated. The instant apparatus may be used in display systems wherein large message symbols may be displayed singularly on the viewing screen 51 and retained for continued viewing by utilization of electrostatic charges on the storage mesh 53 created thereon in response to excitation to the selected portion 14:: of electron flow 14. An individual character shaped beam or portion 14a may be. selected from a plurality of such beams in the electron fiow 14 generated by the photo-cathode 12. The selection of the portion 14a through the aperture 46 allows it to be directed toward the viewing screen 51 through lens system 56 which not only lenses the cross section, effecting desired cross over, on axis, on both portion 14a and electron beam 64, but also increases the velocity of the electrons and expands the cross-sectional area of the beam or portion 14a sufiiciently to meet the size requirements of the finely displayed image on the screen 51.

Immediately in front of the screen 51 and metallized backing 52 toward the cathode 12 is the storage means or memory screen system including the heretofore enumerated fine Wire mesh 53- coated with insulating target elements 63 and fine wire mesh collector screen 54. This general assembly of elements is old in the art of cathode ray storage tubes which utilize a writing beam and a reading beam. In the present invention the writing beam 14a is derived from primary beams or electron flow 14, and the reading beam or electron beam 64 is derived from the thermionic cathode emitter 60. The cathode 60 shown in detail in Figures 6 and 7 may in clude a metallic cup 70, a heater element 71 and the stated oxide coated surface 72. Electrical energy is supplied to the heater element 71 through a pair of conductor leads 80 and 81. A plan view of the cathode surface 72 is shown in Figure 6. The outside diameter, for example, may be approximately 0.1 inch and the center opening 86 about 0.02 inch. In this embodiment, for simplicity of illustration, it is advantageous to generate and control the writing and reading beam 14a and 64, respectively, about the common optical axis of the tube 20. The cathode assembly 60, therefore, is supported coaxially with the optical axis 15 and is provided with opening 86 through the center of the cathode. The opening 86 as stated heretofore is aligned to encompass and aid the aperture 46 in selecting and permitting passage of a character shaped beam 14a therethrough and is coaxial with the axis 15.

Under ordinary circumstances the current density of character shaped beam 14a would be insuflicient to energize the phosphor 51 to the desired light levels primarily due to the relatively low level electron emission capabilities of photo-cathodes, and secondly because it may be desired to expand the initial individual character beam size from approximately 0.010 inch at the time it leaves the photo-cathode 12, to perhaps 100 times this dimension when displayed on the screen 51. Through the use of a high potential, low current beam 14a, 8. control charge pattern may be applied to the surface material 63 of the grid 53 and which in turn controls the passage of the much slower, but higher density, electrons of the reading beam 64.

When a writing pulse is applied to photo-cathode 12 through a capacitor 90 from pulse generator 91, a pulse is also applied to the intensifier 57 through a capacitor 92. After the low current beam 14a passes through the barrier mesh 58 and comes under the influence of the intensifier 57, the beam 14a potential will have attained the level necessary to induce conductivity in the surface material 63, and further produces secondary emission upon being subjected to bombardment by the high energy incident electrons.

The surface material 63, such as talc or other knownmaterials, is a dielectric material having a high specific resistance. Induced conductivity, on the other hand, is brought about because of the matrix structure of solid material. The molecules composing the material form a matrix structure which occupies only a small fraction of its apparent volume. When bombarded by high energy electrons, large numbers of electrons are freed from their molecular bonds to constitute electrons raised to the conduction band energy level. By means of a suitable potential gradient between the dielectric material 63 and the collector mesh 54 the freed electrons are attracted through the molecular matrix of the material 63 and toward the collector mesh 54.

Under the infiuenceof potentials applied to the lens system 56, electrons emitted from the surface 72 of the cathode 60 are directed uniformly over the entire storage surface 63, of the grid structure 53, thereby developing a visible image of the charged pattern on the storage mesh 53'.

The theory of operation and an example of the operating parameters of the storage means necessary in the performance of the memory system included in this display device will be found in a published book by John Wiley & Sons, Inc., New York, N. Y., entitled Storage Tubes and Their Basic Principles, authored by M. Knoll and B. Kazan. The operation of the control elements selected for the present tube application is described on pages 78 through 81 of the above book.

The particular embodiment of the invention illustrated and described herein is illustrative only and the invention includes such other modifications and equivalents as may readily appear to those skilled in the art, Within the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In an evacuated container comprising photo-cathode means positioned at one end thereof for generating and projecting electron flow, a target at the other end capable of responding to electrons, amplifying means interposed in the path of and generally coaxially with the electron flow intermediate the target and the photo-cathode means for effecting amplification of the electron flow, said amplifying means including a thermionic emitter capable of producing an electron beam on a path coaxial with the electron flow, means responding to the electron flow for modulating the electron beam of the emitter.

2. In an evacuated container comprising photo-cathode means positioned at one end thereof for generating and projecting electron flow, a target at the other end capable of responding to electrons, an apertured electrode disposed in the path of the electron flow for selectively limiting the cross section of the electron flow therethrough, amplifying means interposed in the path of the electron flow intermediate the apertured electrode and the target for effecting amplification of the electron flow, said amplifying means including a thermionic emitter capable of producing an electron beam, means responding to the electron flow for modulating the electron beam of the emitter.

3. In an evacuated container having a longitudinal axis comprising photo-cathode means positioned at one end thereof for generating and projecting electron fiow along said axis, a target at the other end capable of responding to electrons, amplifying means interposed in the path of the electron flow intermediate the target and the photo-cathode means for effecting amplification of the electron flow, said amplifying means including a thermionic emitter capable of producing an electron beam, said emitter being disposed coaxially with said axis, means responding to the electron flow for modulating the electron beam of the emitter.

4. In an evacuated container having a target at one erating an electron flow at the other end thereof, and utilizing therebetwe'en aflrst deflection means, an apertured electrode presenting an aperture, said electrode being positioned intermediate thefirst deflection means and the target, said first deflection means being capable of deflecting the beam to position a desired portion thereof through said aperture of said apertured electrode, the improvement comprising means adjacent said apertured electrode and positioned intermediate said apertured electrode and said target, said means including an electronto -light converter positioned in the path of and responsive to excitation by said electron flow, a light transparent conductor positioned contiguous said converter and intermediate it and the target, and a photoconductive means positioned contiguous the opposingtsurface of said conductor, a plurality of mutually insulated conductors having one extremity thereof positioned contiguous the free surface of said photoconductive means, discrete thermionic emissive elements disposed upon the opposing extremity of said conductors, and a heating means positioned adjacent said thermionic emitting elements for heating said thermionic emissive elements.

'5. The invention of claim 4 wherein the means adjacent the apertured electrode is positioned transversely across the electron flow and parallel to the .apertured electrode, said means further having a cross-sectional area at least as great as the aperture.

6. In an evacuated container having a target at one end thereof and a photo-cathode means capable of generating an electron flow at the; other end thereof, and utilizing therebetween a first deflection means,- an aper-' tured electrode presenting an aperture, said electrode of through said 'aperture of said apertured electrode, the;

improvement comprising means intermediate the electrode and the target for amplifying the electron flow, said means including an annular thermionic emitter capable of electron beam generation, said emitter being adapted to permit passage of electron flow therethrough, a lensing means" and a storage means both positioned intermediate the emitter and the target, the lensing rneansbeing adjacent the emitter and being adapted'to cause appropriate lensing action and cross over of each the electron flow and the electron beam, said storage means being capable of responding to store the response of said electron flow thereon, and said electron beam being capable of shadowing said stored response onto said target.

7. The invention of claim 6 wherein the electron flow is projected generally along the longitudinal axis of the container and the apertured electrode and the means for amplifying the electron flow are all positioned coaxially with respect to the longitudinal axis.

References Cited in the file of this patent.

UNITED STATES PATENTS 2,717,971 Sheldon Sept. 13, 1955 

